1. Field of the Invention
The present invention relates to a semiconductor device manufacturing, and more particularly to a cylindrical capacitor with hemi-spherical grain(HSG) silicon on its inner surfaces and a method for fabricating thereof.
2. Description of the Related Art
With the recent increase of integration density of a DRAM, a cell size and an area to be occupied by a capacitor of the DRAM cell tend to reduce, respectively. The capacitor is made of two opposite electrodes and a dielectric film disposed therebetween. As well known in the art, capacitor needs a minimum level of charge storage capacitance.
The capacitance is related to the dielectric thickness, dielectric permittivity and available surface areas. As is well known, the capacitance is proportional to dielectric permittivity and available surface areas and inversely proportional to dielectric thickness.
One way to increase capacitance in a given cell area is to form a thin dielectric film. Another way is to use a high dielectric film having high dielectric permittivity such as BST. Alternative approach is to increase the surface areas of the capacitor by increasing the topology such as a stacked capacitor. Such stacked capacitors include, for examples double-stacked, fin stacked, cylindrical, spread-stacked, and box structured capacitors.
Since both outer and inner surfaces can be utilized as an effective capacitor area, the cylindrical structure is favorably suitable to the three-dimensional stacked capacitor, and is more particularly suitable for an integrated memory cell. Recently, new technologies have been developed for increasing the effective surface area by modifying the surface morphology of the polysilicon storage electrode itself by engraving or controlling the nucleation and growth condition of polysilicon. A hemispherical-grain(HSG) polysilicon layer can be deposited over a storage node to increase surfaces area and capacitance.
A reference is made to the U.S. Pat. No. 5,827,766 by Lou entitled as "Method for fabricating cylindrical capacitor for a memory cell". The above cited reference forms HSG silicons on an inner surface of a cylindrical capacitor.
There are some problems with above cited reference and other methods for forming a cylindrical capacitor with HSG silicon. For example, HSG silicon may be sequestered from the capacitor after formation thereof during subsequent cleaning process using chemical etchant. As a result, sequestered HSG silicons degrade reliability of the capacitor.
Accordingly, there is a strong need for a method for forming a reliable capacitor with increased surface area in a given cell area by forming HSG silicon.